Feed fingers are utilized on automatic screw machines and the like for successively pushing or feeding segments of a continuous length of stock material to a collet of the tool. The bar stock is gripped inside the finger which is able to develop sufficient frictional contact therebetween in order to move the bar stock into the collet on the forward stroke, and when engaged by the collet, the feed finger is retracted to its initial position by sliding rearwardly over the bar stock. A machine operation then takes place at the forward end of the bar stock and following the machining operation, the stock is cut off and the feeding operation is repeated. The interior of the feed finger must have some bar engaging surface which will grip the bar to move it forwardly yet will release the bar to slide rearwardly without scratching or marring of the bar stock material. At the same time, it is desirable to have a feed finger which will readily adapt to feeding a variety of sizes and shapes of bar stock material due to the cost of manufacturing such devices.
Prior feed fingers have been proposed having a slot which opens in the front end of the tube so that the forward end of the tube tends to collapse radially for resiliently gripping the bar stock. Other feed devices have been proposed including leaf springs which resiliently grip the bar stock and have adjustable tensioning means provided by a rotatable sleeve which adjusts the leaf springs. However, since the bar stock is gripped by the feed finger only adjacent the front end thereof, these devices require special guide bushings in the rear portion of the feed finger to insure that the bar stock is maintained centered in the feed finger.
Cage-type feed fingers have been heretofore proposed having a plurality of longitudinal slots spaced around the periphery of the finger which are crimped to adapt the feed finger to a particular size and shape of bar stock material. However, these feeders are not entirely suitable for hex, square or rectangular shaped bar stock since the edges or corners of such stock fit in the slots and the crimped flats often mar and scratch the flats on which they bear. As a result, cage-type pushers are generally used only for round stock.